Hidehiko Yoshida1, Shin Takeuchi2 and Yasumitsu Fukuzawa1
1National Research Institute for Metals, Tokyo
Wire specimens of nickel solid solutions were strained in tension at various temperatures between liquid helium and 500°K to investigate the effect of solute atoms on the mechanical properties of nickel. The solute elements added were Al, Cr, Si, Sb and Ti; they have wide solubility limits in nickel, and their atomic sizes are largely different each other.
Main results obtained are as follows: (1) The temperature dependence of yield stress became more pronounced with increasing solute concentration, as generally observed in FCC alloys. At the high temperature, however, the yield stress still continued decreasing up to 500°K. This behavior is different from the ordinary FCC alloys. (2) The hardening effect of the solute elements was the highest in Sb atom and increased in the order of Al, Cr, Si, Ti and Sb. Some correlation was found between the hardening effect and the atomic size of solute element. (3) The yield stress at 0°K obtained by extrapolation of the σ y-T curve was related to the solute concentration by the equation σ y ∝ cn, where n was a constant between 2/3 and 1 in each alloy system and became larger in the harder alloy. (4) Activation volumes were determined by the strain rate change method. They turned out to be an order of magnitude larger than the value that is expected when the rate determining process is the interaction between the dislocation and each solute atom. (5) The results (3) and (4) cannot be explained by the existing theories on solid solution hardening.
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